Customization of "upload form"

Using only SPD on a MOSS site, is it possible to customize the default formshown when users do a single or multiple file upload into a DocLib?

The problem we are trying to solve is that we have a required field in DocLibwhich is a lookup into a custom list, but here could be hundreds of items in thelist. Thus, we would like to filter or cascade the drop-down on the upload formwhich populates this required field in the DocLib.

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